The disclosure relates to a method and an apparatus for control of a fluid conveying system, comprising at least one pump, at least one consumer as well as at least one armature as an actuator, wherein pressure and volume flow rate of the consumer are controllable.
The closed-loop-control of the process variables of the volume flow rate and thus also of the pressure is the standard task of final controlling devices in technical process installations. Valves or armatures with for example electric or pneumatic drives, also known as control valve or armature with actuator, are preferably used as final controlling devices. Their adjustable flow resistances affect the volume flow rate and the pressure within the installation.
Besides the valves, pumps are the most important components of an installation, as they are causing the movement of fluid. Among the wide range of possible pump designs, the centrifugal pump with drive, in most cases an electric motor with a frequency converter, is the standard solution in many areas of application. Closed-loop-control of process variables by means of a pump can be achieved via the rotation speed of the pump. Just like the stroke or the valve/armature position in case of a valve, in case of a pump the volume flow rate and thus the pressure is affected by changing the rotation speed. Even though in new technical process installations today the portion of speed controlled drives amounts to about 20% to 25%, these are rarely integrated actively into the process control but are rather employed for stationary correction of the pump operating point.
A large number of applications include closed-loop-control tasks requiring for example a large adjustment range owing to the process variables. This task cannot be realized through closed-loop-control by means of the pump only on the one hand and through closed-loop-control with an armature as actuator only on the other hand. The combined use of pump and valve with associated controller opens up new possibilities in process design. However, by combining the devices the controller design becomes more complex since a multi-variable system with 2 inputs must be dealt with. Besides the coupling of the process variables, dead-times often occur in technical process installations, which additionally complicates the closed-loop-control task.